This removes all the need of threading, which removes the contention on the GIL
lock.

Taking S2Test.test_check_output_tee_large as baseline, numbers are
real/user/sys in seconds:
Ubuntu workstation: ~25x  2.4/1.9/1.5 -> 0.10/0.70/0.02
OSX 10.6 laptop:    ~40x  6.4/5.3/3.9 -> 0.15/0.80/0.07
Cygwin on win7:      ~4x  2.8/2.2/1.3 -> 0.60/0.16/0.30

R=dpranke@chromium.org
BUG=
TEST=


Review URL: http://codereview.chromium.org/8462008

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@109283 0039d316-1c4b-4281-b951-d872f2087c98